This invention relates to a method of adjusting the position of a light source in a convergence device employing a spheroidal mirror, wherein the convergence device is used, for example, in an exposure apparatus, a solar simulator, or the like.
A conventional method of this kind, is shown in FIG. 7, in which a discharge tube c is arranged such that the vicinity of the tip e of its cathode d is positioned at a first focal point b of a spheroidal mirror a so that light from the discharge tube c is made to converge at a second focal point f of the spheroidal mirror a. The discharge tube c is illuminated and at the same time a blackboard h is positioned in a plane at right angles to the optical axis g, wherein the plane includes the second focal point f. Then the discharge tube c is moved and adjusted so that the light form the discharge tube c is made to converge on the second focal point f marked on the blackboard h.
However, the conventional method described above has disadvantages in that the discharge tube itself has to be moved and adjusted by examining the blackboard from an angle with respect to the optical axis of the spheroidal mirror which is illuminated by a light of high brightness from the discharge tube so that the light from the discharge tube is focused on the second focal point. Because this adjustment has to take place from an angle, it is difficult to focus accurately on the second focal point without considerable training. Further, at the same time an extinction filter must be positioned for eye protection from a light of high brightness. Additionally, it is impossible to adjust the position of the discharge tube in the type of integrator lens optics in which light from the discharge tube is received on an integrator lens.